lotusdocs Begin fixing landing customization

There is a surprising amount of content that depends on $.Site.Data.landing. This is bad and should be removed or made to use something default-but-changeable This changeset does exactly that. I've also reworked the way that iamge compare is checked for, which makes it possible to use it in the body content as well later as a shortcode.

This also begins the process of making all scripts fingerprintable for SRI.

TODO:

[x] Reduce uneccesary calls to $.Page.Scratch.Get and related.
[ ] add a way to set the default configuration for image comparisons (simple now)
[x] Move the script at the end into app.js (w/a check that we have indeed added the script)
[x] Pet the dog & drink eggnog.

Changes

Move around template logic for the Image Comparison script inclusion. Adding to the end is the right way to do it.
Rename landing.yaml to landing_default.yaml -> This should actually be in data/lotusdocs to namespace it away but I didn't want to make any sudden movements.
Fixed up references to $.Site.Data.landing to one.
Made templates relative to their config data. This allows for multiple instances of each that do not interfere with one another.

fixes #143 and future-proofs it a bit.